• The Journal of the Acoustical Society of Korea
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• v.28 no.6
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• pp.491-498
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• 2009

This paper presents the design method of an impedance matching network using an isolation transformer and the Chebyshev filter function for the high efficiency and the flat power driving of an underwater acoustic piezoelectric transducer. The proposed impedance matching network is designed for minimizing the reactance component of transducer and having the flat power response in the wide frequency range. We design a low pass filter with ladder-type circuit using the Chebyshev function as standard prototype filter function. In addition, we design the impedance matching network which is suitable for the equivalent circuit of transducer and the turn ratio of transformer through the bandpass frequency transformation. The proposed method is applied to the simulated dummy load of the tonpilz-type transducer operating in the middle frequency range. The simulation results are compared with the measured characteristics and the validity of the proposed method is verified.

• Journal of Advanced Navigation Technology
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• v.27 no.6
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• pp.849-854
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• 2023

In this paper, a high-efficiency power amplifier was designed by applying the operating point Class J using LDMOS(laterally diffused metal oxide semiconductor) and optimizing the output matching circuit so that the second harmonic impedance becomes the reactance impedance. The designed power amplifier has a frequency of 108 ~ 110 MHz, Characteristics of PAE(power added efficiency) is 71.5% at P_SAT output (54.5 dBm), 55.5% at P_1dB output (51.5 dBm), and 24.38% at 45 dBm. The CSB(carrier with sideband) amplifier, which is the reference signal in the spatial modulation method, has an operating output of 45 dBm ~ 35 dBm, and linear SDM(sum in the depth of modulation) characteristics(40% ± 0.3%) were obtained. We measure the characteristics in amplitude modulation according to the bias operating point of the power amplifier for CSB and propose the optimal operating point to obtain linear modulation characteristics.

• Tuberculosis and Respiratory Diseases
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• v.87 no.2
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• pp.165-175
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• 2024

Background: The prevalence of small airway dysfunction (SAD) in patients with chronic obstructive pulmonary disease (COPD) across different ethnicities is poorly understood. This study aimed to estimate the prevalence of SAD in stable COPD patients. Methods: We conducted a cross-sectional study of 196 consecutive stable COPD patients. We measured pre- and post-bronchodilator (BD) lung function and respiratory impedance. The severity of COPD and lung function abnormalities was graded in accordance with the Global Initiative for Chronic Obstructive Lung Disease (GOLD) guidelines. SAD was defined as either difference in whole-breath resistance at 5 and 19 Hz > upper limit of normal or respiratory system reactance at 5 Hz < lower limit of normal. Results: The cohort consisted of 95.9% men, with an average age of 66.3 years. The mean forced expiratory volume 1 second (FEV₁) % predicted was 56.4%. The median COPD assessment test (CAT) scores were 14. The prevalence of post-BD SAD across the GOLD grades 1 to 4 was 14.3%, 51.1%, 91%, and 100%, respectively. The post-BD SAD and expiratory flow limitation at tidal breath (EFL_T) were present in 62.8% (95% confidence interval [CI], 56.1 to 69.9) and 28.1% (95% CI, 21.9 to 34.2), respectively. COPD patients with SAD had higher CAT scores (15.5 vs. 12.8, p<0.01); poor lung function (FEV₁% predicted 46.6% vs. 72.8%, p<0.01); lower diffusion capacity for CO (4.8 mmol/min/kPa vs. 5.6 mmol/min/kPa, p<0.01); hyperinflation (ratio of residual volume to total lung capacity % predicted: 159.7% vs. 129%, p<0.01), and shorter 6-minute walk distance (367.5 m vs. 390 m, p=0.02). Conclusion: SAD is present across all severities of COPD. The prevalence of SAD increases with disease severity. SAD is associated with poor lung function and higher symptom burden. Severe SAD is indicated by the presence of EFL_T.

• Tuberculosis and Respiratory Diseases
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• v.45 no.2
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• pp.351-359
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• 1998

Background: The effects of exercise on pulmonary function are complex and have been the subject of many investigations. But, there has been disputes about the effect of exercise on spirometric parameters and there is no study about the effect of exercise on IOS(Impulse Oscillometry)parameters. IOS, a new method of pulmonary function test, is based on the relationship between the pressure and flow oscillation which is produced by applying sinusoidal pressure oscillation to the respiratory system via the mouth. Method: Fifty-nine young adults without respiratory symptoms were divided into three groups according to degree of exercise(hard exercise group: mean exercise time is over three hours per week at least for the last one month, light exercise group : between thirty minutes to three hours, nonexercise group : less than thirty minutes) and undertaken pulmonary function test(simple spirometry and IOS). Results: The effects of exercise on spirometric parameters; percentage of predictive value of forced vital capacity(FVC % pred) was higher in hard exercise group than nonexercise group(hard exercise group: $102.4{\pm}14.8$, nonexercise group: $93.7{\pm}9.9$, p=0.017), but there was no significant difference in percentage of predicted value of forced expiratory volume in one second(FEV 1 % pred) and percentage of predicted value of forced expiratory flow 50% (FEF 50% pred) between groups. The effects of exercise on IOS parameters: Reactance at 5Hz(X5) was significantly lower in hard exercise group than nonexercise group(hard exercise group: $-0.166{\pm}0.123hPa/1/s$, nonexercise group: $-0.093{\pm}0.036hPa/1/s$, p=0.006) but there was no significant difference in central resistance(Rc), peripheral resistance(Rp), resonance frequency(RF) and resistance at 5Hz, 20Hz between groups. Conclusion: Hard exercise increased FVC % pred on spirometric parameters and decreased reactance at 5Hz(X5) on IOS parameters.

• Asia pacific journal of information systems
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• v.19 no.4
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• pp.77-100
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• 2009

Information Systems (IS) is an essential tool for any organizations. The last decade has seen an increasing body of knowledge on IS usage. Yet, IS often fails because of its misuse or non-use. In general, decisions regarding the selection of a system, which involve the evaluation of many IS vendors and an enormous initial investment, are made not through the consensus of employees but through the top-down decision making by top managers. In situations where the selected system does not satisfy the needs of the employees, the forced use of the selected IS will only result in their resistance to it. Many organizations have been either integrating dispersed legacy systems such as archipelago or adopting a new ERP (Enterprise Resource Planning) system to enhance employee efficiency. This study examines user resistance prior to the adoption of the selected IS or ERP system. As such, this study identifies the importance of managing organizational resistance that may appear in the pre-adoption context of an integrated IS or ERP system, explores key factors influencing user resistance, and investigates how prior experience with other integrated IS or ERP systems may change the relationship between the affecting factors and user resistance. This study focuses on organizational members' resistance and the affecting factors in the pre-adoption context of an integrated IS or ERP system rather than in the context of an ERP adoption itself or ERP post-adoption. Based on prior literature, this study proposes a research model that considers six key variables, including perceived benefit, system complexity, fitness with existing tasks, attitude toward change, the psychological reactance trait, and perceived IT competence. They are considered as independent variables affecting user resistance toward an integrated IS or ERP system. This study also introduces the concept of prior experience (i.e., whether a user has prior experience with an integrated IS or ERP system) as a moderating variable to examine the impact of perceived benefit and attitude toward change in user resistance. As such, we propose eight hypotheses with respect to the model. For the empirical validation of the hypotheses, we developed relevant instruments for each research variable based on prior literature and surveyed 95 professional researchers and the administrative staff of the Korea Photonics Technology Institute (KOPTI). We examined the organizational characteristics of KOPTI, the reasons behind their adoption of an ERP system, process changes caused by the introduction of the system, and employees' resistance/attitude toward the system at the time of the introduction. The results of the multiple regression analysis suggest that, among the six variables, perceived benefit, complexity, attitude toward change, and the psychological reactance trait significantly influence user resistance. These results further suggest that top management should manage the psychological states of their employees in order to minimize their resistance to the forced IS, even in the new system pre-adoption context. In addition, the moderating variable-prior experience was found to change the strength of the relationship between attitude toward change and system resistance. That is, the effect of attitude toward change in user resistance was significantly stronger in those with prior experience than those with no prior experience. This result implies that those with prior experience should be identified and provided with some type of attitude training or change management programs to minimize their resistance to the adoption of a system. This study contributes to the IS field by providing practical implications for IS practitioners. This study identifies system resistance stimuli of users, focusing on the pre-adoption context in a forced ERP system environment. We have empirically validated the proposed research model by examining several significant factors affecting user resistance against the adoption of an ERP system. In particular, we find a clear and significant role of the moderating variable, prior ERP usage experience, in the relationship between the affecting factors and user resistance. The results of the study suggest the importance of appropriately managing the factors that affect user resistance in organizations that plan to introduce a new ERP system or integrate legacy systems. Moreover, this study offers to practitioners several specific strategies (in particular, the categorization of users by their prior usage experience) for alleviating the resistant behaviors of users in the process of the ERP adoption before a system becomes available to them. Despite the valuable contributions of this study, there are also some limitations which will be discussed in this paper to make the study more complete and consistent.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.26 no.10
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• pp.885-894
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• 2015

In this paper, it can be applied to a walkie-talkie, the RFID / USN 920 MHz band(917~923.5 MHz) and WiFi 2.4GHz band(2.4~2.483 5GHz) return loss is 10 dB over the band, on-board dual band with omni-directional radiation characteristics is proposed. The basic structure designed antenna is used meander monopole antenna. It was used as double stubs and tabs for antenna designs that meet the criteria proposed. The double stub and the tab affects the reactance of the antenna to form a common-mode and differential-mode in the stub to improve the antenna characteristics and return loss in the bandwidth, gain and radiation characteristics. The system size of walkie-talkie is $52{\times}77mm^2$, the size of the antenna is limited to $52{\times}15mm^2$, the thickness of FR4 dielectric substrate is 0.8 mm, FR4 dielectric constant 4.4 is used. For experimental results, the return loss is measured more than 10 dB, the maximum gain is measured 1.95 dB, the maximum bandwidth is measured 360 MHz, the radiation characteristic is measured omni-directional. By a walkie-talkie terminal design applying the results of the paper, the handset's price competitiveness and production efficiency can be improved.

• Clinical and Experimental Pediatrics
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• v.50 no.9
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• pp.862-867
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• 2007

Purpose : The impulse oscillometry (IOS) is applicable to young children because it requires minimal cooperation and a non-invasive method to measure the mechanics of respiratory system. This study aimed to develop the reference values in school-aged children in Korea, using IOS which is a modification of forced oscillation technique (FOT). Methods : Measurements were performed in 92 previously untrained healthy children, aged 7 to 12 years old, using IOS. We analyzed the relationships between the data about their age, height, weight, body surface area (BSA), body mass index (BMI) and the result of IOS using the linear regression test. Results : The success rate of IOS was 92.4%. Stepwise multiple regression of resistance of respiratory system (Rrs) and reactance of respiratory system (Xrs) in natural form for age, height, weight, BSA, BMI showed that height was the most significant predictor and altogether of 5 variables explained the Rrs and Xrs most. Our regression equations at multiple frequencys were comparable to published reference values, especially about the Rrs obtained at 5 Hz. Conclusion : IOS is a feasible method to measure the respiratory resistance in untrained children. We got the reference values using IOS and it seems to be useful to diagnose a variety of respiratory diseases.

• Clinical and Experimental Pediatrics
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• v.54 no.2
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• pp.64-68
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• 2011

Purpose: The normal values for lung resistance and lung capacity of children, as determined by impulse oscillometry (IOS), are different for children of different ethnicities. However, reference values there is no available reference value for Korean preschool children have yet to be determined. The aim of the present study was to determine the normal ranges of IOS parameters in Korean preschool children. Methods: A total of 133 healthy Korean preschool children were selected from 639 children (aged 3 to 6 years) who attended kindergarten in Seongnam, Gyeonggi province, Korea. Healthy children were defined according to the European Respiratory Society (ERS) criteria. All subjects underwent lung function tests using IOS. The relationships between IOS value (respiratory resistance (Rrs) and reactance (Xrs) at 5 and 10 Hz and resonance frequency (RF)) and age, height, and weight were analyzed by simple linear and multiple linear regression analyses. Results: The IOS success rate was 89.5%, yielding data on 119 children. Linear regression identified height as the best predictor of Rrs and Xrs. Using stepwise multiple linear regressions based on age, height, and weight, we determined regression equations and coefficients of determination ($R^2$) for boys ($Rrs_5=1.934-0.009{\times}Height$, $R^2$=12.1%; $Xrs_5=0.774+0.006{\times}Height-0.002{\times}Age$, $R^2$=20.2% and for girls $(Rrs_5=2.201-0.012{\times}Height$, $R^2$=18.2%; $Xrs_5=-0.674+0.004{\times}Height$, $R^2$=10.5%). Conclusion: This study provides reference values for IOS measurements of normal Korean preschool children. These provide a basis for the diagnosis and monitoring of preschool children with a variety of respiratory diseases.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.11
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• pp.138-144
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• 2017

With the increase in power consumption due to the surge in the demand for power, it is necessary to improve the quality or design of the power (supply) for the purpose of reducing the energy consumption and so reduce the power loss. The switchboard is a mechanical device that receives electricity from the electricity generation facilities of KEPCO and divides it into the facilities required for each building. Switchboards generally consist of enclosures, switches, power conductors, and control components. This study deals with energized power conductors, which constitute the main element in the switchboard. Through the measurement of the effective ac resistance, it was confirmed that the vertical array structure of the conventional type plate conductor is inefficient. If the effective AC resistance increases significantly, the sectional area of the conductor becomes relatively large due to the skin effect. In this study, we studied the energy and material savings that could be obtained using the asterisk (*) array structure, which minimizes the effective ac resistance by reducing the skin effect. The core technology principle of this study is the energy saving switchgear based on conductor resistance reduction technology utilizing the asterisk array structure. The present invention involves a plate-shaped conductor arrangement structure capable of canceling out the magnetic field generated on each of the plate conductors (rst or abc) of the AC power supply in the power distribution panel by mutual action. The effect of this structure is to reduce the amount of inductive reactance due to the increase in the cross-sectional area and reduction of the effective AC resistance.

• Journal of Platform Technology
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• v.9 no.2
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• pp.38-45
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• 2021

A frequently used bioimpedance analytical method in Korea is the segmental multi-frequency BIA (SMF-BIA) method, but it is not directly determined at a segmented impedance. This study was to compare SMF-BIA determinations with direct segmented determinations for accuracy and appropriateness of segment parameters. This study is to compare the segment parameters, accuracy and appropriateness of the multi-frequency segmental bioimpedance analysis. To this end, 108 elderly individuals were measured. Segmented bioelectrical measurements obtained from a SMF-BIA (Inbody S10) at 50 kHz and measured with a phase sensitive single frequency device (SF-BIA, bia-101, RJL / akern systems) were compared. The significant difference (%) was demonstrated between single - and multiple frequency determinations of the right upper limb (R = 35.5 ± 6.2%, P < 0.001; Xc = 2.7 ± 7.6%, P < 0.01), left upper limb difference (R= 33. 9 ± 6.0%, P < 0.001; Xc = 2.8 ± 8.3%, P < 0.01), right lower limb difference (R = 18.6 ± 4.3%, P < 0.001; Xc = 25.8 ± 10.0%, P < 0.001), left lower limb difference (R = 18.0 ± 4.7%, P < 0.001; Xc = 31.8%). Of the results determined with the two BIA methods, the impedance measurements of the limbs and whole body showed a high correlation (RA: R = 0. 950, LA: R = 0. 949, RL: R = 0.899, LL: R = 0.88), and in the agreement test, the impedance values of the upper limbs and whole body also showed strong agreement (ICC > 0.9), but in the Xc, the correlation was weak. In conclusion, it was found that although bioimpedance devices had significantly different characteristics and inconsistent cross sectionally, there was a high population level agreement in the upper and lower extremities in determining segmental resistance value changes. But a large error was found on the trunk. Further studies were needed for reducing the error.